Engines, including diesel engines, gasoline engines, gaseous fuel powered engines, and other engines known in the art ignite injections of fuel to produce heat. In one example, fuel injected into a combustion chamber of the engine is ignited by way of a spark plug. The heat and expanding gases resulting from this combustion process may be directed to displace a piston or move a turbine blade, both of which can be connected to a crankshaft of the engine. As the piston is displaced or the turbine blade is moved, the crankshaft is caused to rotate. This rotation may be utilized to directly drive a device such as a transmission to propel a vehicle, or a generator to produce electrical power.
During operation of the engine described above, a complex mixture of air pollutants is produced as a byproduct of the combustion process. These air pollutants are composed of solid particulate matter and gaseous compounds including nitrous oxides (NOx). Due to increased attention on the environment, exhaust emission standards have become more stringent and the amount of solid particulate matter and gaseous compounds emitted to the atmosphere from an engine is regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to reduce the production of these pollutants is to introduce a lean air/fuel mixture into the combustion chambers of the engine. This lean mixture, when ignited, burns at a relatively low temperature. The lowered combustion temperature slows the chemical reaction of the combustion process, thereby decreasing the formation of regulated emission constituents. As emission regulations become stricter, leaner and leaner mixtures are being implemented.
Although successful at reducing emissions, very lean air/fuel mixtures are difficult to ignite. That is, the single point arc from a conventional spark plug may be insufficient to initiate and/or maintain combustion of a mixture that has little fuel (compared to the amount of air present). As a result, the emission reduction available from a typical spark-ignited engine operated in a lean mode may be limited. In addition, conventional spark plugs suffer from low component life due to the associated high breakdown voltage requirement of the arc.
One attempt at improving combustion initiation of a lean air/fuel mixture is described in U.S. Pat. No. 3,934,566 (the '566 patent) issued to Ward on Jan. 27, 1976. The '566 patent discloses a system for use with a controlled vortex combustion chamber (CVCC) engine having a main combustion chamber, a pre-combustion chamber, and one spark plug located in each of the combustion and pre-combustion chambers. The system couples high frequency electromagnetic energy (RF energy) into the pre-combustion chamber either through the associated spark plug or in the vicinity of the spark plug tip. The RF energy is produced by magnetrons or microwave solid-state devices, and can act in conjunction with the mechanically linked action of the typical distributor rotor shaft to obtain timing information therefrom. The system concentrates on using the RF energy to create a plasma mixture of air and fuel before, after, or before and after the instant the pre-combustion chamber is fired by means of an arc at the spark plug tip. The presence of the microwave energy at or near the spark plug tip modifies the voltage required for firing and facilitates ignition of a lean air/fuel mixture. It may even be possible to eliminate the arc altogether by using microwave sources in a pulsed mode and by designing the spark plug tip in such a manner that it both couples microwave energy efficiently to the air-fuel plasma mixture as a whole, as well as produces large electric fields at the highly localized region of the spark plug tip. The RF energy is coupled to the spark plug in the pre-combustion chamber, as compared to the combustion chamber, because the pre-combustion chamber contains an ignitable richer mixture.
Although the system of the '566 patent may improve combustion of a lean air/fuel mixture and, in one embodiment, may have an affect on the damage caused by high temperature arcing, the system may still be problematic and have limited applicability. For example, the amount of power and the voltage level required to produce a plasma of the air/fuel mixture and to ignite the mixture may be at least partially dependent on the volume of the mixture. That is, a large combustion chamber volume may require a large amount of power and high voltage levels to sufficiently ionize and ignite the air/fuel mixture within the chamber. Thus, although the system of the '566 patent may, in one embodiment, reduce the power requirement through the use of an engine's pre-combustion chamber, the required power and voltage levels may still be very high. And, in engines without pre-combustion chambers, the system of the '566 patent may require prohibitively large amounts of power and excessive voltage levels to ionize and ignite a lean air/fuel mixture within the larger combustion chambers.
The igniter of the present disclosure solves one or more of the problems set forth above.